"The P-10 Power Tank can fill a 33" tire from 15 to 30 PSI, 26 times before running empty."

Not to shabby....

Here is a good article, old but has some info on what to expect for re-filling an such.

Power Tank Review - ORN

Everything i have read indicates they are safe but do some 'googling' so you feel confident with it in the back.

 

CO2 is the way to go IMO. Pretty cheap (about $15 to fill a 15# tank) and they last a while. One 15# tank lasts me a whole day of wheeling. My rig uses A LOT of air too. I have F and R air actuated lockers, active air suspension (automatically levels right to left and front to back-- lowers for ease of entry/exit, raises up for stream crossings) and CTIS-- and that is with 40" tires airing up and down a few times during the day (from down around 7 psi wheeling up to about 15psi for highway and fast trails.
I have an Oasis compressor with 2 dedicated batteries for OBA but I don't like the noise of it kicking on and off all of the time. I had planned to use the CO2 for backup and found that I liked the peace and quiet of the CO2 over the compressor.
You just can't beat it.
My rig: